Fuel injected engines use injectors to introduce fuel into the combustion chambers of the engine. The injectors may be hydraulically or mechanically actuated with mechanical, hydraulic, or electrical control of fuel delivery. For example, a mechanically-actuated, electronically-controlled fuel injector includes a plunger movable by a cam-driven rocker arm to pressurize fuel within a bore of the injector. One or more electronic devices disposed within the injector are then actuated to deliver the pressurized fuel into the combustion chambers of the engine at one or more predetermined conditions.
One example of a mechanically-actuated, electronically-controlled fuel injector is described in U.S. Pat. No. 6,856,222 (the '222 patent) issued to Forck on Feb. 15, 2005. The '222 patent describes a fuel injector having a spring-biased, solenoid-controlled spill valve and a spring-biased, solenoid-controlled injection control valve. Both the spill valve and the injection control valve are associated with a cam-driven plunger and a control chamber of a valve needle. As the plunger is initially forced by a cam into a bore within the fuel injector, fuel within the bore flows past the spill valve to a low pressure drain. When the spill valve is electrically closed during further movement of the plunger into the bore, pressure within the bore builds. When an injection of fuel is desired, the injection control valve is electronically moved to connect the control chamber to the low pressure drain, thus permitting movement of the valve needle away from a seating to commence injection. To end injection, the injection control valve disconnects the control chamber from the low pressure drain to return the valve needle to its seating.
Although the injector of the '222 patent may sufficiently inject fuel into the combustion chambers of an engine, it may be limited when injecting small quantities of fuel. In particular, because both start of injection and end of injection are controlled with the same injection control valve, the valve element of the injection control valve may not have reached a point of stability after initiating start of injection when it must again move to end the injection. This lack of stability may create unpredictable and unrepeatable injection characteristics that could cause improper, unpredictable, unstable, and/or undesired operation of the engine.
The control method of the present disclosure solves one or more of the problems set forth above.